This invention is particularly useful in beverage container packaging machines such as that shown and disclosed in the inventors co-pending patent application Ser. No. 08/118,111 filed Sep. 2, 1993, the disclosure of which is incorporated herein by reference for purposes of providing an adequate background for the present invention. Even though the present invention will be described in the context of such a packaging machine, it should be understood that the invention has application wherever plastic bumpers or guides are to be affixed to a metal rail or frame.
As disclosed in the above referenced patent application, in beverage container packaging machines, containers such as cans or bottles typically are conveyed in mass along a conveyor toward a packaging section of the machine. As the containers approach the packaging section, they encounter a plurality of lanes formed by an array of spaced metal rails. The rails function to herd the containers into the lanes and to direct them laterally toward the packaging mechanism. Although the detailed operation of packaging machines can vary dramatically, most utilize this type of guide rail assembly to align the containers and herd them in the appropriate direction for packaging.
When employing guide rails to herd beverage containers in a packaging machine, it is desirable to affix a plastic bumper or guide to each rail extending along the length thereof. Usually, these guides are configured as narrow strips that extend along the upper edge or the upper and lower edge portions of each rail. The guides serve a number of purposes. Since they are usually fabricated of a low friction plastic material such as teflon, the guides reduce significantly the friction between the moving beverage containers and the guide rails as the containers progress along the lanes. This enhances the efficiency of the packaging process and helps to prevent jams that otherwise can occur. Further, the guides are narrower and far less abrasive than the metal rails to which they are attached. Accordingly, they do not tend to abrade or scrape the painted or paper labels from the beverage containers as the containers move along the lanes. The labels and other indicia on the containers are thus protected by the plastic guides. In addition, the guides reduce significantly the operating noise of the machine by preventing the beverage containers from banging against the metal rails as the containers move along their lanes.
In the past, plastic guides have been attached to their metal rails by a variety of methods. In some instances, the guides and the rails have been machined and threaded at spaced intervals along their lengths. The guides are then affixed to the rails by flat headed bolts that are threaded into the rails with their heads countersunk into the guides to avoid an obtrusion. While this method works, its implementation is labor intensive, requiring perhaps hundreds of individual holes to be drilled, tapped, and countersunk in the guides and rails for receiving the bolts. Further, the requirement of separate bolts adds cost, increases the time required to affix the guides to their rails, and can become a problem since the bolts can work loose and their countersunk heads tend to collect dirt. In addition, the guides must be thick enough to accommodate the countersunk heads, requiring more material and impacting the spacing between adjacent rails.
In another method of affixing the guides to their rails, the rails are machined to have spaced tangs that extend upwardly from the top edges of the rails. The plastic guide members are then formed to extend along the top edges of the rails and are machined with slots that receive the spaced tangs of the rails. The tangs are bored and threaded and flat headed bolts are used to fix the guides to their rails at the positions of the tangs. As with the previous method, this method is labor intensive since the rails must be machined to exhibit tangs and the tangs and guides must be machined and threaded to receive the attaching bolts. Each of the many bolts must be separately installed, requiring significant time, and the bolts can come loose over time. The plastic guides might also be bonded directly to their metal rails with an appropriate adhesive. However, such bonding is prohibitively expensive and can require a significant investment of time and resources.
Clearly, there exists a need for an improved plastic guide assembly that fastens quickly, easily, and securely along the length of metal guide rails, that imposes minimum machining requirements for its attachment to the rail, is thinner than prior art guides, and that requires no screws or additional hardware for attachment. It is to the provision of such a self fastening guide for guide rails that the present invention is primarily directed.